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#include "race.h"
#include <bits/stdc++.h>
#define sp <<" "
#define el <<"\n"
#define S second
#define F first
#define pb push_back
#define all(ar) ar.begin(),ar.end()
#define pii pair<int,int>
using namespace std;
using ll = long long;
using ld = long double;
const int mxr = 200005;
const int big = 2000000999;
int n,k,ans = big;
vector<vector<pii>> g;
bitset<mxr> ded;
void dfs(int v,int p,vector<int> &sz){
sz[v] = 1;
for(pii r: g[v]){
if(r.F == p || ded[r.F]) continue;
dfs(r.F,v,sz);
sz[v] += sz[r.F];
}
return;
}
int fcen(int v,int p,int lim,vector<int> &sz){
for(pii r: g[v]){
if(r.F == p || ded[r.F]) continue;
if(sz[r.F] > lim) return fcen(r.F,v,lim,sz);
}
return v;
}
void fil(int v,int p,int cost,int dep,unordered_map<int,int> &dis,unordered_map<int,int> &cum){
if(cost > k) return;
if(cum.count(k - cost)) ans = min(ans, dep + cum[k - cost]);
dis[cost] = dis.count(cost) ? min(dis[cost],dep) : dep;
for(pii r: g[v]){
if(r.F == p || ded[r.F]) continue;
fil(r.F,v,cost + r.S,dep+1,dis,cum);
}
return;
}
void decompose(int v){
vector<int> sz(n+1);
dfs(v,-1,sz);
int lim = (sz[v]/2);
int cen = fcen(v,-1,lim,sz);
ded[cen] = 1;
unordered_map<int,int> cum;
for(pii r: g[cen]){
if(ded[r.F]) continue;
unordered_map<int,int> dis;
fil(r.F,cen,r.S,1,dis,cum);
for(pii x: dis) cum[x.F] = cum.count(x.F) ? min(cum[x.F],x.S) : x.S;
}
if(cum.count(k)) ans = min(ans,cum[k]);
for(pii r: g[cen]){
if(!ded[r.F]) decompose(r.F);
}
}
int best_path(int N, int K, int H[][2], int L[])
{
n = N;
k = K;
g.assign(n,{});
for(int i = 1; i < n; i++){
int a = H[i-1][0], b = H[i-1][1], c = L[i-1];
g[a].pb({b,c});
g[b].pb({a,c});
}
decompose(0);
return ans == big ? -1 : ans;
}
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